This invention relates to the preparation of polyether resins. In a specific aspect, the invention relates to the reaction of an epoxy resin with a polyhydric alcohol so as to prepare a polyether resin essentially free of epoxide groups.
Polyether resins prepared by the reaction of an epoxy resin and an aliphatic polhydric alcohol are useful resin constituents of coating formulations. U.S. Pat. No. 2,731,444 describes various reaction products of epoxy resins and aliphatic polyhydric alcohols in terms of the equivalent ratios of the reactants and the desired remaining epoxide groups, if any, in the product. Examples 42-49 of the patent describe a process in which an equivalent excess of a polyhydric alcohol is reacted with an epoxy resin to prepare a reaction product containing both unreacted epoxy and unreacted hydroxyl groups. The described process involves very high reaction temperatures, such as 250.degree. C., and does not react all the epoxide groups present. Further heating of the epoxide-containing product of Example 42 produced a hard, infusible "gel." Such a gel is not suitable as a starting material for the preparation of curable coating compositions. It has been found that the use of an even greater ratio of hydroxy to epoxy and a lower temperature also results in a gelled product.
It is therefore an object of the invention to provide a process for preparing a reaction product of an epoxy resin and a polyhydric alcohol which has essentially no epoxide groups. In one embodiment, it is an object of the invention to provide a relatively low-temperature reaction process for preparing a polyester resin having essentially no epoxide groups.